Understanding the Science: What is the Most Hydrating Drink?

October 1, 2025 •

4 min read

While most people assume plain water is the most hydrating, a 2016 study published in the American Journal of Clinical Nutrition ranked several beverages using a 'Beverage Hydration Index' and found milk to be more hydrating than water. To truly understand what is the most hydrating drink, you must look beyond just water.

Quick Summary

Analyzes the most hydrating beverages by exploring how electrolytes, sugar, protein, and fat affect fluid absorption. Compares water, milk, coconut water, and oral rehydration solutions for everyday needs, intense exercise, and recovery.

Key Points

Skim milk is highly hydrating: Studies show milk's combination of electrolytes, protein, and fat helps the body retain fluids more effectively than water, making it excellent for rehydration after intense exercise.
Water is the best for daily needs: For general hydration without significant exertion, plain water remains the healthiest and most cost-effective choice, with no added sugars or calories.
Oral Rehydration Solutions are for severe cases: These medically formulated solutions are specifically designed to treat dehydration from illness like diarrhea and vomiting by maximizing fluid absorption.
Moderate caffeine doesn't dehydrate you: Contrary to popular belief, moderate coffee or tea consumption (around 2-4 cups) does not lead to dehydration and can contribute to your daily fluid intake.
Electrolytes are crucial after intense activity: During prolonged or high-intensity exercise, consuming beverages with electrolytes like sports drinks or coconut water helps replace the minerals lost through sweat.
High-sugar drinks can be counterproductive: While juices contain water, their high sugar concentration can slow hydration by causing the body to pull fluid into the small intestine for dilution.

The Science of Hydration: Why It’s More Than Just Water

For most daily needs, water is sufficient for hydration because it contains no calories or additives. However, the speed and efficiency of fluid absorption depend on more than just the water content. The presence of other nutrients, like electrolytes, carbohydrates, and even protein and fat, can significantly impact how long your body retains fluids. This is measured using the Body Hydration Index (BHI), which compares beverages' effectiveness in maintaining hydration over time against plain water.

Electrolytes are key minerals like sodium and potassium that help regulate the balance of fluids inside and outside of your cells. When we sweat, we lose these crucial electrolytes, which need to be replaced. Beverages containing these minerals can help the body retain water more effectively, leading to prolonged hydration.

Milk's Surprising Hydration Power

Research from Scotland’s St. Andrews University revealed that both skim and full-fat milk are more hydrating than plain water. This effect is attributed to milk's specific composition. It contains lactose (a sugar), protein, and fat, which collectively slow the rate at which the stomach empties fluids. This slower digestion allows for a more sustained release and absorption of water, helping the body retain fluids longer and producing less urine. Furthermore, milk's natural sodium content acts like a sponge, helping to hold water in the body.

Oral Rehydration Solutions for Severe Dehydration

For moderate to severe dehydration, especially from illness involving vomiting or diarrhea, Oral Rehydration Solutions (ORS) are superior. These are specifically formulated with a precise balance of water, glucose, sodium, and potassium to enhance fluid absorption in the intestines. This mechanism takes advantage of the sodium-glucose co-transport system, which pulls water into the bloodstream alongside these molecules. The World Health Organization (WHO) and UNICEF endorse ORS for treating dehydration effectively. While commercial products like Pedialyte are available, ORS is fundamentally a medical solution and not intended for casual, everyday hydration.

Coconut Water and Sports Drinks

Both coconut water and commercial sports drinks are often marketed as powerful hydrators due to their electrolyte content. Coconut water is a natural source of potassium and other electrolytes, making it a refreshing option for replenishing minerals lost during moderate sweating. However, its sodium content is often lower than sports drinks. For intense, prolonged exercise lasting over an hour, or in hot conditions, sports drinks like Gatorade can be beneficial. They contain both carbohydrates and electrolytes to replenish energy stores and replace lost fluids more efficiently than plain water. However, many commercial sports drinks also contain high levels of added sugar, which isn't necessary for light or moderate activity.

Common Beverages and the Hydration Equation

Coffee and Tea: The long-held belief that caffeinated beverages are dehydrating is largely a myth for moderate consumption. In fact, a study showed that moderate coffee consumption (around 2-4 cups) is just as hydrating as water. The diuretic effect of caffeine only becomes significant at much higher doses. It's best to stick with decaf options if you are particularly sensitive to caffeine or trying to maximize hydration.
100% Fruit Juice: Pure fruit juices are hydrating due to their high water content and natural sugars, but the high sugar concentration can be counterproductive. When consumed in large quantities, the body pulls water into the intestine to dilute the sugar, which can actually draw fluids away from other cells. It's best to limit intake and choose 100% juice without added sugars.
Herbal Teas: Caffeine-free herbal teas are an excellent, flavorful way to boost your daily fluid intake. They are primarily water but also contain antioxidants and other beneficial plant compounds.
Broth-based Soups: For situations like illness or during winter, soups are a great way to consume both fluids and electrolytes, particularly sodium, which helps with water retention.

How to Hydrate Effectively

Drink throughout the day: Don't wait until you feel thirsty, as this is a sign you are already starting to be dehydrated.
Monitor urine color: A pale yellow color indicates proper hydration, while darker urine suggests you need more fluids.
Adapt your beverage choice: Match your drink to your activity level and health status. Water is great for daily needs, while milk or an electrolyte drink can be better after strenuous exercise.
Balance intake: Ensure your fluid intake from all sources—drinks and foods—is balanced. Water-rich foods like fruits and vegetables contribute significantly to your daily hydration.


Beverage	Primary Use Case	Key Hydration Feature	Calories (per cup)	Notes
Water	Everyday Hydration	Zero calories, simple fluid replacement	0	The gold standard for daily use.
Skim Milk	Post-Exercise Recovery	Electrolytes, protein, and fat slow stomach emptying for longer hydration.	~80	Offers nutrients for muscle repair in addition to fluids.
Oral Rehydration Solution (ORS)	Severe Dehydration/Illness	Formulated glucose and electrolytes maximize intestinal fluid absorption.	Varies	Best for illness-related fluid loss; use under medical guidance.
Coconut Water	Moderate Exercise	Natural source of potassium and electrolytes.	~45	A natural, lower-sugar alternative to sports drinks.
Sports Drinks	Intense/Prolonged Exercise	Electrolytes and carbohydrates replenish minerals and energy.	Varies	Check sugar content; unnecessary for light activity.

Conclusion

While water is the indispensable foundation of a healthy hydration strategy, the question of what is the most hydrating drink has a nuanced answer. The ideal beverage depends on your body's specific needs at a given moment. For general, day-to-day fluid intake, water is the best choice due to its purity and lack of calories. However, after a hard workout, a glass of milk offers superior rehydration and nutritional benefits. For illness-related dehydration, a carefully balanced Oral Rehydration Solution is the most effective and medically supported option. By understanding the physiological factors that influence how your body absorbs fluids, you can make smarter, more effective choices to maintain optimal hydration.

FluidLogic: Electrolytes vs Water offers additional details on the strategic use of electrolytes for performance and recovery.

Frequently Asked Questions

Yes, for rehydration after significant fluid loss, some studies have shown milk to be more hydrating than plain water. Its composition of lactose, protein, fat, and electrolytes helps the body retain fluids longer.

You should choose an electrolyte drink over water during or after intense and prolonged exercise (over 60 minutes), especially in hot conditions, or when recovering from illness involving diarrhea or vomiting.

Yes, in moderation. The diuretic effect of caffeine is not significant enough at typical consumption levels (around 2-4 cups) to cause dehydration. Both coffee and tea can contribute to your daily fluid intake.

For a sick child with moderate dehydration due to vomiting or diarrhea, an Oral Rehydration Solution (ORS) like Pedialyte is the best choice. It has the proper balance of sugar and salts for effective fluid replacement.

Yes, many fruits and vegetables, like watermelon and cucumber, have a very high water content (often over 85%) and contain electrolytes, making them excellent for contributing to your overall fluid intake.

Coconut water is a natural source of electrolytes, particularly potassium, and can be a good, lower-sugar alternative to a sports drink for moderate activity. However, it may have less sodium than is needed after an intense, salty sweat.

Yes, for mild dehydration, you can create a simple electrolyte solution at home using clean water, a pinch of salt, and a little fruit juice or sugar. For more serious cases, commercial or medical-grade ORS is recommended.